The present invention is directed to an expansion dowel made up of a sleeve-shaped dowel body and an expansion element located in the central bore within the dowel body. The dowel body is provided with axially extending slits extending from its leading end and the body is radially expandable in the axially extending region of the slits by axially displacing the expansion element.
One requirement of expansion dowels is a simple installation procedure. Such a requirement is fulfilled mainly in known expansion dowels by an impact expansion operation. This type of expansion dowel includes a sleeve-shaped steel dowel body with a central bore having a section extending in the installation direction which tapers conically outwardly toward the leading end and an expansion element or body in the form of a cylindrically member which may also be made of steel. To expand the dowel body in a borehole in a receiving material, such as concrete, masonry or the like, the dowel body is provided with an axial slit extending from its leading end and preferably the expansioh element is driven forwardly by impact into the tapered section of the dowel bore. A considerable disadvantage of this type of expansion dowel is its high fabrication cost which results due to the large material expenditure and also because of the formation of the tapered central bore.
Another known expansion dowel type based on the same anchoring procedure is notable, because of its simpler production. This expansion dowel consists of a sleeve-shaped dowel body with a continuous cylindrically shaped bore and with axial slits provided in its axial region at the leading end, that is, the end first inserted into the receiving material. To anchor such a dowel, a plastically deformable expansion element, such as formed of lead or plastics material, is positioned in the bore of the dowel body and is upset or deformed. This procedure leads to an expansion of the dowel body in the receiving material borehole. In this anchoring procedure the radial deformation of the dowel body takes place in a non-uniform manner, since the greatest deformation occurs at the location where the resistance of the receiving material is smallest.
Another problem impeding the anchoring values of such an expansion dowel results from the escape of the material forming the expansion element, since it can flow during the deformation step through the axial slit and may also partially flow out of the dowel bore counter to the insertion direction. The region and degree of deformation of the dowel body during the expansion procedure is largely undefined.